I had the Exonys and it was terrible, barely lasted a day. Imported the SD865+ version (N9860) and it's like chalk and cheese. Far smoother, faster and the battery life is instantly better.
Yet another Samsung screw up. You shouldn't have to import and lose warrenty to get a phone that works properly. The company are clueless. Removing this, removing that. Removal of SD card slots will be the end of Samsung for me.
All I can say is I've had both .... and the SD is miles ahead. It also has a brighter more colourful display too.
Jerryrig did a test on Youtube comparing thermals and battery life on both, and there was a 20% difference.
Maybe the overall issue is that they have used a multitude of different components and you actually get a good one if you are lucky!